Receipt Working Group Roger Fajman
Internet Draft National Institutes of Health
Expires: 11 October 1997 6 April 1997
An Extensible Message Format
for Message Disposition Notifications
draft-ietf-receipt-mdn-03.txt
Status of this Memo
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Abstract
This memo defines a MIME content-type that may be used by a mail
user agent (UA) or electronic mail gateway to report the disposition
of a message after it has been sucessfully delivered to a recipient.
This content-type is intended to be machine-processable. Additional
message headers are also defined to permit Message Disposition
Notifications (MDNs) to be requested by the sender of a message.
The purpose is to extend Internet Mail to support functionality
often found in other messaging systems, such as X.400 and the
proprietary "LAN-based" systems, and often referred to as "read
receipts," "acknowledgements," or "receipt notifications." The
intention is to do this while respecting the privacy concerns that
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have often been expressed when such functions have been discussed in
the past.
Because many messages are sent between the Internet and other
messaging systems (such as X.400 or the proprietary "LAN-based"
systems), the MDN protocol is designed to be useful in a multi-
protocol messaging environment. To this end, the protocol described
in this memo provides for the carriage of "foreign" addresses, in
addition to those normally used in Internet Mail. Additional |
attributes may also be defined to support "tunneling" of foreign
notifications through Internet Mail. |
1. Introduction
This memo defines a MIME [5] content-type for message disposition |
notifications (MDNs). An MDN can be used to notify the sender of a
message of any of several conditions that may occur after successful
delivery, such as display of the message contents, printing of the
message, deletion (without display) of the message, or the
recipient's refusal to provide MDNs. The
"message/disposition-notification" content-type defined herein is
intended for use within the framework of the "multipart/report"
content type defined in RFC 1892 [7]. |
This memo defines the format of the notifications and the RFC 822
headers used to request them.
1.1 Purposes
The MDNs defined in this memo are expected to serve several pur-
poses:
(a) Inform human beings of the disposition of messages after
succcessful delivery, in a manner which is largely independent
of human language;
(b) Allow mail user agents to keep track of the disposition of
messages sent, by associating returned MDNs with earlier
message transmissions;
(c) Convey disposition notification requests and disposition
notifications between Internet Mail and "foreign" mail systems
via a gateway;
(d) Allow "foreign" notifications to be tunneled through a MIME-
capable message system and back into the original messaging
system that issued the original notification, or even to a
third messaging system;
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(e) Allow language-independent, yet reasonably precise, indications
of the disposition of a message to be delivered.
1.2 Requirements
These purposes place the following constraints on the notification
protocol:
(a) It must be readable by humans, as well as being machine-
parsable.
(b) It must provide enough information to allow message senders (or
the user agents) to unambiguously associate an MDN with the
message that was sent and the original recipient address for
which the MDN is issued (if such information is available),
even if the message was forwarded to another recipient address.
(c) It must also be able to describe the disposition of a message
independent of any particular human language or of the ter-
minology of any particular mail system.
(d) The specification must be extensible in order to accomodate
future requirements.
2. Requesting Message Disposition Notifications
Message disposition notifications are requested by including a
Disposition-notification-to header in the message. Further informa-
tion to be used by the recipient's UA in generating the MDN may be
provided by including Original-recipient and/or Disposition-
notification-options headers in the message.
2.1 The Disposition-Notification-To Header
A request that the receiving user agent issue message disposition
notifications is made by placing a Disposition-notification-to
header into the message. The syntax of the header, using the ABNF |
of RFC 822 [2], is |
mdn-request-header = "Disposition-notification-to" ":" 1#mailbox
The address token is as specified in RFC 822 [2]. |
The presence of a Disposition-notification-to header in a message is
merely a request for an MDN. The recipients' user agents are always
free to silently ignore such a request. Alternatively, an explicit
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denial of the request for information about the disposition of the
message may be sent using the "denied" disposition in an MDN. |
One and only one MDN may be issued on behalf of each particular
recipient by their user agent. That is, once an MDN has been issued
on behalf of a recipient, no further MDNs may be issued on behalf of
that recipient, even if another disposition is performed on the
message. However, if a message is forwarded, a "processed" MDN may |
been issued for the recipient doing the forwarding and the recipient |
of the forwarded message may also cause an MDN to be generated.
While Internet standards normally do not specify the behavior of
user interfaces, it is strongly recommended that the user agent
obtain the user's consent before sending an MDN. This consent could
be obtained for each message through some sort of prompt or dialog
box, or globally through the user's setting of a preference. The
user might also indicate globally that MDNs are never to be sent or
that a "denied" MDN is always sent in response to a request for an
MDN.
It is also strongly recommended that MDNs never be sent automati-
cally if the address in the Disposition-notification-to header
differs from the address in the Return-path header (see RFC 822
[2]). In this case, confirmation from the user should be obtained, |
if possible. If obtaining consent is not possible (e.g., because
the user is not online at the time), then no MDN should be sent.
It is also recommended that confirmation from the user always be
obtained (or no MDN sent) if there is no Return-path header in the
message, or if there is more than one distinct address in the
Disposition-notification-to header. The comparison of the addresses
should be done using only the addr-spec (local-part "@" domain)
portion, excluding any phrase and route. If the message contains
more than one Return-path header, the implementation may pick one to
use for the comparison, or treat the situation as a failure of the
comparison.
The reason for not automatically sending an MDN if the comparison
fails or more than one address is specified is to reduce the pos- |
sibilities for mail loops and use of MDNs for mail bombing. |
A message that contains a Disposition-notification-to header SHOULD
also contain a Message-ID header as specified in RFC 822 [2]. This |
will permit automatic correlation of MDNs with original messages by
user agents.
If it is desired to request message disposition notifications for
some recipients and not others, two copies of the message should be
sent, one with an Disposition-notification-to header and one
without. Many of the other headers of the message (e.g., To, cc) |
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will be the same in both copies. The recipients in the respective |
message envelopes determine for whom message disposition notifica-
tions are requested and for whom they are not. If desired, the
Message-ID header may be the same in both copies of the message.
Note that there are other reasons (e.g., bcc) to send multiple |
copies of a message with slightly different headers, so that may |
result in more than two copies of a message being sent, some with a |
Disposition-notification to header and some without. |
2.2 The Disposition-Notification-Options Header
Future extensions to this specification may require that information |
be supplied to the recipient's UA for additional control over how
and what MDNs are generated. The Disposition-notification-options
header provides an extensible mechanism for such information. The |
syntax of this header, using the ABNF of RFC 822 [2], is |
Disposition-notification-options =
"Disposition-notification-options" ":"
disposition-notification-parameters
Disposition-notification-parameters = parameter *(";" parameter)
parameter = attribute "=" importance "," 1#value
importance = "R" / "O"
The definitions of attribute and value are as in the definition of
the Content-type header in RFC 2046 [5]. |
An importance of R indicates that interpretation of the parameter is
required for proper generation of an MDN in response to this re-
quest. If a UA does not understand the meaning of the parameter, it
MUST not generate an MDN in response to the request. An importance
of O (the letter) indicates that a UA that does not understand the
meaning of this parameter MAY generate an MDN in response anyway,
ignoring the value of the parameter.
No parameters are defined in this specification. Parameters may be
defined in the future by later revisions or extensions to this
specification. Parameter attribute names beginning with "X-" will
never be defined as standard names; such names are reserved for
experimental use. MDN parameter names NOT beginning with "X-" MUST
be registered with the Internet Assigned Numbers Authority (IANA)
and described in a standards-track RFC or an experimental RFC |
approved by the IESG. |
If a required parameter is not understood or contains some sort of |
syntax error, the receiving UA SHOULD issue an MDN with a disposi- |
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tion type of "failure" and include a Failure field that further |
describes the problem. MDNs with the a disposition type of |
"failure" and a "Failure" field MAY also be generated when other |
types of syntax errors in the parameters of the Disposition- |
notificatiob-options header. |
2.3 The Original-Recipient Header
Since electronic mail addresses may be rewritten while the message
is in transit, it is useful for the original recipient address to be
made available by the delivering MTA. The MTA may be able to obtain
this information from the ORCPT parameter of the SMTP MAIL FROM
command, as defined in RFC 1891 [8]. If this information is avail- |
able, the delivering MTA SHOULD insert an Original-recipient header
into the message and delete any other Original-recipient headers |
that occur in the message. The syntax of this header, using the |
ABNF of RFC 822 [2], is as follows |
original-recipient-header =
"Original-Recipient" ":" address-type ";" generic-address
The address-type and generic-address token are as as specified in
the description of the Original-recipient field in section 3.2.3.
The purpose of carrying the original recipient information and
returning it in the MDN is to permit automatic correlation of MDNs
with the original message on a per-recipient basis.
|
|
2.4 Use with the Message/Partial Content Type |
|
The use of the headers Disposition-notification-to, Disposition- |
notification-options, and Original-Recipient with the MIME |
Message/partial content type (RFC #### [#]) requires further defini- |
tion. If these headers occur along with the other headers of a |
message/partial fragment message, they pertain to an MDN to be |
generated for the fragment. If these headers occur in the headers |
of the "inner" or "enclosed" message (using the terms of RFC #### |
[#]), they pertain to an MDN to be generated for the reassembled |
message. Section 7.2.2.1 of RFC #### [#]) is amended to specify |
that, in addition to the headers specified there, the three headers |
described in this specification are to be appended, in order, to the |
headers of the reassembled message. Any occurances of the three |
headers defined here in the headers of the initial enclosing message |
must not be copied to the reassembled message. |
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3. Format of a Message Disposition Notification
A message disposition notification is a MIME message with a top-
level content-type of multipart/report (defined in RFC 1892 [7]). |
When a multipart/report content is used to transmit an MDN:
(a) The report-type parameter of the multipart/report content is
"disposition-notification".
(b) The first component of the multipart/report contains a human-
readable explanation of the MDN, as described in RFC 1892 [7]. |
(c) The second component of the multipart/report is of content-type
message/disposition-notification, described in section 3.1 of
this document.
(d) If the original message or a portion of the message is to be
returned to the sender, it appears as the third component of
the multipart/report.
NOTE: For message dispostion notifications gatewayed from
foreign systems, the headers of the original message may not be
available. In this case the third component of the MDN may be
omitted, or it may contain "simulated" RFC 822 headers which
contain equivalent information. In particular, it is very
desirable to preserve the subject and date fields from the
original message.
The MDN MUST be addressed (in both the message header and the
transport envelope) to the address from the Disposition-
notification-to header which from the original message for which the
MDN was generated.
The From field of the message header of the MDN MUST contain the
address of the person on whose behalf the message disposition
notification is being issued.
The envelope sender address (i.e., SMTP MAIL FROM) of the MDN should
be null (<>), specifying that no Delivery Status Notification
messages or other messages indicating successful or unsuccessful
delivery are to be sent in response to an MDN.
A message disposition notification MUST NOT itself request an MDN.
That is, it MUST NOT contain a Disposition-notification-to header.
The Message-ID header (if present) for an MDN MUST be different from
the Message-ID of the message for which the MDN is being issued.
A particular MDN describes the disposition of exactly one message
for exactly one recipient. Multiple MDNs may be generated as a
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result of one message submission, one per recipient. However, due
to various circumstances, MDNs may not be generated for some
recipients for which MDNs were requested.
3.1 The message/disposition-notification content-type
The message/disposition-notification content-type is defined as
follows:
MIME type name: message
MIME subtype name: disposition-notification
Optional parameters: none
Encoding considerations: "7bit" encoding is sufficient and
MUST be used to maintain readability
when viewed by non-MIME mail
readers.
Security considerations: discussed in section 6 of this memo|.
The message/disposition-notification report type for use in the
multipart/report is "disposition-notification".
The body of a message/delivery-status consists of one or more
"fields" formatted according to the ABNF of RFC 822 header "fields"
(see [2]). Using the ABNF of RFC 822, the syntax of the |
message/disposition-notification content is as follows:
disposition-notification-content = [ reporting-ua-field CRLF ]
[ mdn-gateway-field CRLF ]
[ original-recipient-field CRLF ]
final-recipient-field CRLF
[ original-message-id-field CRLF ]
disposition-field CRLF
*( failure-field CRLF ) |
*( error-field CRLF ) |
*( warning-field CRLF ) |
*( extension-field CRLF )
3.1.1 General conventions for fields
Since these fields are defined according to the rules of RFC 822
[2], the same conventions for continuation lines and comments apply. |
Notification fields may be continued onto multiple lines by begin-
ning each additional line with a SPACE or HTAB. Text which appears
in parentheses is considered a comment and not part of the contents
of that notification field. Field names are case-insensitive, so
the names of notification fields may be spelled in any combination
of upper and lower case letters. Comments in notification fields
may use the "encoded-word" construct defined in RFC 2047 [6]. |
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3.1.2 "*-type" subfields
Several fields consist of a "-type" subfield, followed by a semi-
colon, followed by "*text". For these fields, the keyword used in
the address-type or MTA-type subfield indicates the expected format
of the address or MTA-name that follows.
The "-type" subfields are defined as follows:
(a) An "address-type" specifies the format of a mailbox address.
For example, Internet Mail addresses use the "rfc822" address- |
type.
address-type = atom
(b) An "MTA-name-type" specifies the format of a mail transfer
agent name. For example, for an SMTP server on an Internet
host, the MTA name is the domain name of that host, and the
"dns" MTA-name-type is used.
mta-name-type = atom
Values for address-type and mta-name-type are case-insensitive.
Thus address-type values of "RFC822" and "rfc822" are equivalent.
The Internet Assigned Numbers Authority (IANA) will maintain a
registry of address-type and mta-name-type values, along with
descriptions of the meanings of each, or a reference to a one or
more specifications that provide such descriptions. (The "rfc822"
address-type is defined in RFC 1891 [8].) Registration forms for |
address-type and mta-name-type appear in RFC 1894 [9]. |
IANA will not accept registrations for any address-type name that
begins with "X-". These type names are reserved for experimental
use.
3.1.3 Lexical tokens imported from RFC 822
The following lexical tokens, defined in RFC 822 [2], are used in |
the ABNF grammar for MDNs: addr-spec, atom, CHAR, comment, CR,
CRLF, DIGIT, LF, linear-white-space, SPACE, text. The date-time
lexical token is defined in RFC 1123 [3]. |
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3.2 Message/disposition-notification Fields
3.2.1 The Reporting-UA field
reporting-ua-field = "Reporting-UA" ":" ua-name
ua-name = *text
The Reporting-UA field is defined as follows:
A MDN describes the disposition of a message after it has been
delivered a recipient. In all cases, the Reporting-UA is the UA
that performed the disposition described in the MDN. This field is
optional, but recommended. For Internet Mail user agents, it is
recommended that this field contain both the DNS name of the par-
ticular instance of the UA that generated the MDN and the name of
the product. For example,
Reporting-UA: rogers-mac.dcrt.nih.gov (Foomail 97.1)
3.2.2 The MDN-Gateway field
The MDN-Gateway field indicates the name of the gateway or MTA that
translated a foreign (non-Internet) message disposition notification
into this MDN. This field MUST appear in any MDN which was trans-
lated by a gateway from a foreign system into MDN format, and MUST
NOT appear otherwise.
mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name
For gateways into Internet Mail, the MTA-name-type will normally be |
"smtp", and the mta-name will be the Internet domain name of the
gateway.
3.2.3 Original-Recipient field
The Original-Recipient field indicates the original recipient
address as specified by the sender of the message for which the MDN
is being issued. For Internet Mail messages the value of the
Original-Recipient field is obtained from the Original-Recipient
header from the message for which the MDN is being generated. If
there is no Original-Recipient header in the message, then the
Original-Recipient field MUST be omitted. If there is an Original-
Recipient header in the original message (or original recipient
information is available some other way), then the Original-
Recipient field must be supplied.
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original-recipient-field =
"Original-Recipient" ":" address-type ";" generic-address
generic-address = *text
The address-type field indicates the type of the original recipient
address. If the message originated within the Internet, the
address-type field field will normally be "rfc822", and the address
will be according to the syntax specified in RFC 822 [2]. The value |
"unknown" should be used if the Reporting UA cannot determine the
type of the original recipient address from the message envelope.
This address is the same as that provided by the sender and can be
used to automatically correlate MDN reports with original messages
on a per recipient basis.
3.2.4 Final-Recipient field
The Final-Recipient field indicates the recipient for which the MDN
is being issued. This field MUST be present.
The syntax of the field is as follows:
final-recipient-field =
"Final-Recipient" ":" address-type ";" generic-address
The generic-address subfield of the Final-Recipient field MUST
contain the mailbox address of the recipient (from the From header)
as it was when the message was accepted by the UA.
The Final-Recipient address may differ from the address originally
provided by the sender, because it may have been transformed during
forwarding and gatewaying into an totally unrecognizable mess.
However, in the absence of the optional Original-Recipient field,
the Final-Recipient field and any returned content may be the only
information available with which to correlate the MDN with a par-
ticular message recipient.
The address-type subfield indicates the type of address expected by
the reporting MTA in that context. Recipient addresses obtained via
SMTP will normally be of address-type "rfc822".
Since mailbox addresses (including those used in the Internet) may
be case sensitive, the case of alphabetic characters in the address
MUST be preserved.
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3.2.5 Original-Message-ID field
The Original-Message-ID field indicates the message-ID of the
message for which the MDN is being issued. It is obtained from the
Message-ID header of the message for which the MDN is issued. This
field MUST be present if the original message contained a Message-ID
header. The syntax of the field is
original-message-id-field = "Original-Message-ID" ":" msg-id
The msg-id token is as specified in RFC 822 [2]. |
3.2.6 Disposition field
The Disposition field indicates the action performed by the
Reporting-UA on behalf of the user. This field MUST be present.
The syntax for the Disposition field is: |
disposition-field = "Disposition" ":" disposition-type |
1*( "," dispostion-modifier ) |
disposition-type = "displayed" |
/ "processed" |
/ "deleted" |
/ "denied" |
/ "failed" |
|
disposition-modifier = ( "useraction" / "autoaction" ) |
/ ( "usersent" / "autosent" ) |
/ ( "error" / "warning" ) |
/ ( "obsoleted" / "expired" / "terminated" |
) |
/ disposition-modifier-extension |
disposition-modifier-extension = atom |
The disposition-type and disposition-modifier may be spelled in any |
combination of upper and lower case characters. The following |
disposition-types are defined: |
"displayed" The message has been displayed by the UA to someone |
reading the recipient's mailbox. There is no |
guarantee that the content has been read or under-
stood.
|
"processed" The message has been processed in some manner (e.g.,
printed, faxed, forwarded) without being displayed to |
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the user. The user may or may not see the message
later.
|
"deleted" The message has been deleted. The recipient may or |
may not have seen the message. The recipient might
"undelete" the message at a later time and read the
message.
|
"denied" The recipient does not wish the sender to be informed |
of the message's disposition. A UA may also |
siliently ignore message disposition requests in this |
situation. |
|
"failed" A failure occurred that prevented the proper gener- |
ation of an MDN. More information about the cause of |
the failure may be contained in a Failure field. The |
"failed" disposition type is not to be used for the |
situation in which there is is some problem in |
processing the message other than interpreting the |
request for an MDN. The "processed" or other dis- |
position type with appropriate disposition modifiers |
is to be used in such situations. |
|
The following disposition modifiers are defined: |
|
"useraction" The disposition described by the |
disposition type was a result of |
an explicit instruction by the |
user rather than some sort of |
automatically performed action. |
|
"autoaction" The disposition described by the |
disposition type was a result of |
an automatic action, rather than |
an explicit instruction by the |
user for this message. |
|
"Useraction" and "autoaction" are |
mutually exclusive. One or the |
other must be specified. |
|
"usersent" The user explicity gave permis- |
sion for this particular MDN to |
be sent. "Usersent" is meaning- |
ful with "useraction", but not |
with "autoaction". |
|
"autosent" The MDN was sent because the UA |
had previously been configured to |
do so automatically. "Autosent" |
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is meaningful with both "userac- |
tion" and "autoaction". |
|
"Usersent" and "autosent" are |
mutually exclusive. One or the |
other must be specified. |
|
"error" An error of some sort occurred |
that prevented successful |
processing of the message. |
Further information is contained |
in an Error field. |
|
"warning" The message was successfully |
processed but some sort of |
exceptional condition occurred. |
Further information is contained |
in a Warning field. |
|
"obsoleted" The message has been automati-
cally rendered obsolete by
another message received. The
recipient may still access and
read the message later.
"expired" The message has reached its
expiration date and has been
automatically removed from the
recipient's mailbox.
"terminated" The recipient's mailbox has been
terminated and all message in it
automatically removed.
|
"Obsoleted", "expired", and |
"terminated" are to be used with |
the "deleted" disposition type |
and the "autoaction" and |
"autosent" disposition modifiers. |
|
disposition-modifier-extension Additional disposition modifiers |
may be defined in the future by |
later revisions or extensions to
this specification. Disposition
value names beginning with "X-"
will never be defined as standard
values; such names are reserved
for experimental use. MDN
disposition value names NOT
beginning with "X-" MUST be
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registered with the Internet
Assigned Numbers Authority (IANA)
and described in a standards- |
track RFC or an experimental RFC |
approved by the IESG. MDNs with |
disposition value names not
understood by the receiving UA
MAY be silently ignored or placed
in the user's mailbox without
special interpretation. They
MUST not cause any error message
to be sent to the sender of the
MDN.
|
If an UA developer does not wish |
to register the meanings of such |
disposition modifier extensions, |
"X-" modifiers may be used for |
this purpose. To avoid name |
collisions, the name of the UA |
implementation should follow the |
"X-", (e.g. "X-Foomail-fratzed"). |
It is not required that a UA be able to generate all of the possible
values of the Disposition field.
One and only one MDN may be issued on behalf of each particular
recipient by their user agent. That is, once an MDN has been issued
on behalf of a recipient, no further MDNs may be issued on behalf of
that recipient, even if another disposition is performed on the
message. However, if a message is forwarded, a "processed" MDN may |
been issued for the recipient doing the forwarding and the recipient |
of the forwarded message may also cause an MDN to be generated.
|
|
3.2.7 Failure, Error and Warning fields |
|
The Failure, Error and Warning fields are used to supply additional |
information in the form of text messages when the "failure" disposi- |
tion type, "error" disposition modifier, and/or the "warning" |
disposition modifer appear. The syntax is |
|
failure-field = "Failure" ":" *text |
|
error-field = "Error" ":" *text |
|
warning-field = "Warning" ":" *text |
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3.3 Extension fields
Additional MDN fields may be defined in the future by later revi-
sions or extensions to this specification. Extension-field names
beginning with "X-" will never be defined as standard fields; such
names are reserved for experimental use. MDN field names NOT
beginning with "X-" MUST be registered with the Internet Assigned
Numbers Authority (IANA) and described in a standards-track RFC or |
an experimental RFC approved by the IESG. |
Extension MDN fields may be defined for the following reasons:
(a) To allow additional information from foreign disposition
reports to be tunneled through Internet MDNs. The names of
such MDN fields should begin with an indication of the foreign
environment name (e.g. X400-Physical-Forwarding-Address).
(b) To allow transmission of diagnostic information which is
specific to a particular user agent (UA). The names of such
MDN fields should begin with an indication of the UA implemen-
tation which produced the MDN. (e.g. Foomail-information).
If an UA developer does not wish to register the meanings of such
extension fields, "X-" fields may be used for this purpose. To
avoid name collisions, the name of the UA implementation should
follow the "X-", (e.g. "X-Foomail-Log-ID").
4. Timeline of events
The following timeline shows when various events in the processing
of a message and generation of MDNs take place:
--- User composes message
|
|-- User tells UA to send message
|
|-- UA passes message to MTA (original recipient information
| passed along)
|
|-- MTA sends message to next MTA
.
.
.
|-- Final MTA receives message
|
|-- Final MTA delivers message to UA (possibily generating DSN)
|
|-- UA performs automatic processing and generates corresponding
| MDNs ("processed", "deleted", "denied" or "failed" disposition |
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| type with "autoaction" and "autosent" disposition modifiers) |
|
|-- UA displays list of messages to user
|
|-- User selects a message and requests that some action be
| performed on it.
|
|-- UA performs requested action and, with user's permission,
| sends appropriate MDN ("displayed", "processed", "deleted", |
| "denied" or "failure" disposition type with "useraction" and |
| "usersent" or "autosent" disposition modifiers). |
|
|-- User possibly performs other actions on message, but no
| further MDNs are generated. |
5. Conformance and Usage Requirements
A UA or gateway conforms to this specification if it generates MDNs
according to the protocol defined in this memo. It is not necessary
to be able to generate all of the possible values of the Disposition
field.
UAs and gateways MUST NOT generate the Original-Recipient field of
an MDN unless the mail protocols provide the address originally
specified by the sender at the time of submission. Ordinary SMTP
does not make that guarantee, but the SMTP extension defined in RFC
1891 [8] permits such information to be carried in the envelope if |
it is available. The Original-Recipient header defined in this
document provides a way for the MTA to pass the original recipient
address to the UA.
Each sender-specified recipient address may result in more than one
MDN. If an MDN is requested for a recipient that is forwarded to
multiple recipients of an "alias" (as defined in RFC 1891 [8], |
section 7.2.7), each of the recipients may issue an MDN.
Successful distribution of a message to a mailing list exploder may
be considered final disposition of the message. A mailing list
exploder may issue an MDN with a disposition type of "processed" and |
disposition modifiers of "autoaction" and "autosent" indicating that |
the message has been forwarded to the list. In this case, the |
request for MDNs is not propogated to the members of the list.
Alternatively, the mailing list exploder may issue no MDN and
propogate the request for MDNs to all members of the list. The
later behavior is not recommended for any but small, closely knit
lists, as it might cause large numbers of MDNs to be generated and
may cause confidential subscribers to the list to be revealed. It
is also permissible for the mailing list exploder to direct MDNs to
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itself, correlate them, and produce a report to the original sender
of the message.
This specification places no restrictions on the processing of MDNs
received by user agents or mailing lists.
6. Security considerations
The following security considerations apply when using MDNs:
6.1 Forgery
MDNs may be forged as easily as ordinary Internet electronic mail.
User agents and automatic mail handling facilities (such as mail
distribution list exploders) that wish to make automatic use of MDNs
should take appropriate precautions to minimize the potential damage
from denial-of-service attacks.
Security threats related to forged MDNs include the sending of:
(a) A falsified disposition notification when the indicated dis-
position of the message has not actually ocurred,
(b) Unsolicited MDNs
6.2 Confidentiality
Another dimension of security is confidentiality. There may be
cases in which a message recipient does not wish the disposition of
messages addressed to him to be known or is concerned that the
sending of MDNs may reveal other confidential information (e.g.,
when the message was read). In this situation, it is acceptable for
the UA to issue "denied" MDNs or to silently ignore requests for |
MDNs.
If the Disposition-notification-to header is passed on unmodified
when a message is distributed to the subscribers of a mailing list,
the subscribers to the list may be revealed to the sender of the
original message by the generation of MDNs.
In general, any optional MDN field may be omitted if the Reporting
UA site or user determines that inclusion of the field would impose
too great a compromise of site confidentiality. The need for such
confidentiality must be balanced against the utility of the omitted
information in MDNs.
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6.3 Non-Repudiation
Within the framework of today's Internet Mail, the MDNs defined in |
this document provide valuable information to the mail user;
however, MDNs can not be relied upon as a guarantee that a message
was or was not not seen by the recipient. Even if MDNs are not
actively forged, they may be lost in transit. The MDN issuing
mechanism may be bypassed in some manner by the recipient.
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7. Appendix - collected grammar
NOTE: The following lexical tokens are defined in RFC 822: addr-
spec, address, atom, CHAR, comment, CR, CRLF, DIGIT, LF, linear-
white-space, SPACE, text. The date-time lexical token is defined in
RFC 1123 [3]. |
Message headers:
mdn-request-header = "Disposition-notification-to" ":" 1#mailbox
Disposition-notification-options =
"Disposition-notification-options" ":"
disposition-notification-parameters
Disposition-notification-parameters = parameter *(";" parameter)
parameter = attribute "=" importance "," 1#value
importance = "R" / "O"
original-recipient-header =
"Original-Recipient" ":" address-type ";" generic-address
Report content:
disposition-notification-content = [ reporting-ua-field CRLF ]
[ mdn-gateway-field CRLF ]
[ original-recipient-field CRLF ]
final-recipient-field CRLF
[ original-message-id-field CRLF ]
disposition-field CRLF
*( failure-field CRLF ) |
*( error-field CRLF ) |
*( warning-field CRLF ) |
*( extension-field CRLF )
address-type = atom
mta-name-type = atom
reporting-ua-field = "Reporting-UA" ":" ua-name
ua-name = *text
mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name
original-recipient-field =
"Original-Recipient" ":" address-type ";" generic-address
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generic-address = *text
final-recipient-field =
"Final-Recipient" ":" address-type ";" generic-address
disposition-field = "Disposition" ":" disposition-value
|
disposition-field = "Disposition" ":" disposition-type |
1*( "," dispostion-modifier ) |
|
disposition-type = "displayed" |
/ "processed" |
/ "deleted" |
/ "denied" |
/ "failed" |
|
disposition-modifier = ( "useraction" / "autoaction" ) |
/ ( "usersent" / "autosent" ) |
/ ( "error" / "warning" ) |
/ ( "obsoleted" / "expired" / "terminated" ) |
/ disposition-modifier-extension |
|
disposition-modifier-extension = atom |
original-message-id-field = "Original-Message-ID" ":" msg-id
subscriber-address = *text
extension-field = extension-field-name ":" *text
extension-field-name = atom
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8. Appendix - Guidelines for gatewaying MDNs
NOTE: This section provides non-binding recommendations for the
construction of mail gateways that wish to provide semi-transparent
disposition notifications between the Internet and another
electronic mail system. Specific MDN gateway requirements for a
particular pair of mail systems may be defined by other documents.
8.1 Gatewaying from other mail systems to MDNs
A mail gateway may issue an MDN to convey the contents of a "for-
eign" disposition notification over Internet Mail. When there are |
appropriate mappings from the foreign notification elements to MDN
fields, the information may be transmitted in those MDN fields.
Additional information (such as might be needed to tunnel the
foreign notification through the Internet) may be defined in exten-
sion MDN fields. (Such fields should be given names that identify
the foreign mail protocol, e.g. X400-* for X.400 protocol elements)
The gateway must attempt to supply reasonable values for the
Reporting-UA, Final-Recipient, and Disposition fields. These will
normally be obtained by translating the values from the foreign
notification into their Internet-style equivalents. However, some
loss of information is to be expected.
The sender-specified recipient address, and the original message-id,
if present in the foreign notification, should be preserved in the
Original-Recipient and Original-Message-ID fields.
The gateway should also attempt to preserve the "final" recipient
address from the foreign system. Whenever possible, foreign
protocol elements should be encoded as meaningful printable ASCII
strings.
For MDNs produced from foreign disposition notifications, the name
of the gateway MUST appear in the MDN-Gateway field of the MDN.
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8.2 Gatewaying from MDNs to other mail systems
It may be possible to gateway MDNs from the Internet into a foreign
mail system. The primary purpose of such gatewaying is to convey
disposition information in a form that is usable by the destination
system. A secondary purpose is to allow "tunneling" of MDNs through
foreign mail systems, in case the MDN may be gatewayed back into the
Internet.
In general, the recipient of the MDN (i.e., the sender of the
original message) will want to know, for each recipient: the
closest available approximation to the original recipient address,
and the disposition (displayed, printed, etc.).
If possible, the gateway should attempt to preserve the Original-
Recipient address and Original-Message-ID (if present), in the
resulting foreign disposition report.
If it is possible to tunnel an MDN through the destination environ-
ment, the gateway specification may define a means of preserving the
MDN information in the disposition reports used by that environment.
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9. Appendix - Examples
NOTE: These examples are provided as illustration only, and are not
considered part of the MDN protocol specification. If an example
conflicts with the protocol definition above, the example is wrong.
Likewise, the use of *-type subfield names or extension fields in
these examples is not to be construed as a definition for those type
names or extension fields.
|
|
9.1 This is an MDN issued after a message has been displayed to the
user of an Internet Mail user agent.
|
Date: Wed, 20 Sep 1995 00:19:00 (EDT) -0400
From: Joe Recipient <Joe_Recipient@mega.edu>
Message-Id: <199509200019.12345@mega.edu>
Subject: Disposition notification
To: Jane Sender <Jane_Sender@huge.com>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=disposition-notification;
boundary="RAA14128.773615765/mega.edu"
--RAA14128.773615765/mega.edu
The message sent on 1995 Sep 19 at 13:30:00 (EDT) -0400 to
Joe Recipient <Joe_Recipient@mega.edu> with subject "First
draft of report" has been displayed. This is no guarantee
that the message has been read or understood.
--RAA14128.773615765/mega.edu
content-type: message/disposition-notification
Reporting-UA: joes-pc.cs.mega.edu (Foomail 97.1)
Original-Recipient: rfc822;Joe_Recipient@mega.edu
Final-Recipient: rfc822;Joe_Recipient@mega.edu
Original-Message-ID: <199509192301.12345@mega.edu>
Disposition: displayed, useraction, usersent |
--RAA14128.773615765/mega.edu
content-type: message/rfc822
[original message goes here]
--RAA14128.773615765/mega.edu--
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10. Acknowledgments
This document is based on the Delivery Status Notifications docu- |
ment, RFC 1894 [9], by Keith Moore and Greg Vaudreuil. Contribu- |
tions were made by members of the IETF Receipt Working Group, |
including Harald Alverstrand, Ian Bell, Urs Eppenberger, Ned Freed, |
Jim Galvin, Carl Hage, Mike Lake, Keith Moore, Paul Overell, Pete |
Resnick, Chuck Shih. |
[Author's note -- If you would like to be included, let me know and
I will add your name.]
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11. References
[1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, |
USC/Information Sciences Institute, August 1982. |
|
[2] Crocker, D., "Standard for the Format of ARPA Internet Text |
Messages", STD 11, RFC 822, UDEL, August 1982. |
|
[3] Braden, R. (ed.) "Requirements for Internet Hosts - Application |
and Support", RFC 1123, October 1989. |
|
[4] Borenstein, N., Freed, N. "Multipurpose Internet Mail Exten- |
sions (MIME) Part One: Format of Internet Message Bodies", RFC |
12045 Bellcore, Innosoft, April 1996. ##verify## |
[5] Borenstein, N., Freed, N. "Multipurpose Internet Mail Exten- |
sions (MIME) Part Two: Media Types", RFC 2046, Bellcore, |
Innosoft, April 1996. ##verify## |
|
[6] Moore, K. "Multipurpose Internet Mail Extensions (MIME) Part |
Three: Message Header Extensions for Non-Ascii Text", RFC |
2047, University of Tennessee, April 1996. ##verify## |
|
[7] Vaudreuil, G. "The Multipart/Report Content Type for the |
Reporting of Mail System Administrative Messages", RFC 1892,
Octel Network Services, January 1996.
[8] Moore, K. "SMTP Service Extension for Delivery Status |
Notifications", RFC 1891, University of Tennessee, January
1996.
[9] Moore, K. and Vaudreuil, G. "An Extensible Format for Delivery |
Status Notifications, RFC 1894, University of Tennessee, Octel
Network Services, January 1996.
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12. Author's Address
Roger Fajman
National Institutes of Health
Building 12A, Room 3063 |
12 South Drive MSC 5659
Bethesda, Maryland 20892-5659
USA
Email: raf@cu.nih.gov
Voice: +1 301 402 4265
Fax: +1 301 480 6241
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Datatracker
draft-ietf-receipt-mdn-03
Internet-Draft
